1. Field of the Invention
The present invention relates to a light amount adjustment device mounted to an image pickup apparatus or the like.
2. Description of the Related Art
Conventionally, some image pickup apparatus such as a digital camera or a digital single-lens reflex camera is mounted with a mechanical light amount adjustment device such as a shutter device for exposure operation or a diaphragm device for diaphragm operation.
Since recent image pickup devices have high sensitivity, the shutter device is required to operate at high speed to prevent over-exposure at the time of high sensitivity photographing under bright condition. The diaphragm device is required to be driven at high speed and with accuracy in order to shorten a release time lag from when a release button is pressed by a photographer to when an image is actually picked up.
An image pickup apparatus using a galvanic diaphragm device having a diaphragm member of float structure is disclosed in Japanese Patent Publication No. 4247024. Depending on the diaphragm aperture change speed, the diaphragm member of float structure sometimes overshoots a target aperture value. In that case, the time required for photographing becomes long. Thus, the diaphragm device disclosed in Japanese Patent Publication No. 4247024 has a plunger that presses the diaphragm member to stop the diaphragm member.
However, a scratch or dent is sometimes produced at that part of the diaphragm member which is pressed by the plunger. In the case of the diaphragm member which is thin in thickness such as a light-shield member, there is a fear that the diaphragm member does not operate smoothly, so that a light amount adjustment cannot be carried out with accuracy. In addition, a space is required for installation of the plunger.